usleep(3)

💤 usleep(3) — it's giving "pause, bestie" ✨

okay so real quick, the manual name is usleep and it lives in the Library Functions Manual section of the Linux man-pages. Let's get into it 💅

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🌸 NAME 🌸

usleep — suspend execution for microsecond intervals

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📚 LIBRARY 📚

Standard C library (libc, -lc)

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🎀 SYNOPSIS 🎀

#include <unistd.h>

int usleep(useconds_t usec);

✨ Feature Test Macro Requirements for glibc (see feature_test_macros(7)) ✨

usleep():

• Since glibc 2.12:

(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
    || /* glibc >= 2.19: */ _DEFAULT_SOURCE
    || /* glibc <= 2.19: */ _BSD_SOURCE

• Before glibc 2.12:

_BSD_SOURCE || _XOPEN_SOURCE >= 500

like yes you have to define the right macros, it's the price of admission 😭

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🦋 DESCRIPTION 🦋

The usleep() function suspends execution of the calling thread for (at least) usec microseconds. 💤

so lowkey "at least" is doing a lot of work there — the sleep may be lengthened slightly by any system activity, or by the time spent processing the call, or by the granularity of system timers. it's not a precision instrument, bestie, it's a vibe 🌈

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⭐ RETURN VALUE ⭐

The usleep() function returns 0 on success. 🫶

On error, -1 is returned, with errno set to indicate the error. no cap.

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💀 ERRORS 💀

• EINTR — Interrupted by a signal; see signal(7).
• EINVAL — usec is greater than or equal to 1000000. (On systems where that is considered an error.)

not every system thinks EINVAL is an error bestie, so don't @ the ones that just let it slide 🙈

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👑 ATTRIBUTES 👑

For an explanation of the terms used in this section, see attributes(7).

• Interface: usleep()
• Attribute: Thread safety
• Value: MT-Safe

(yes queen, MT-Safe — she's thread safe, we love that for her 💅)

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🧚 STANDARDS 🧚

None.

like… none. she's simply not standardized. iconic behavior honestly 🎀

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🌸 HISTORY 🌸

4.3BSD, POSIX.1-2001. POSIX.1-2001 declares it obsolete, suggesting nanosleep(2) instead. Removed in POSIX.1-2008.

so yeah, officially deprecated, she got removed, it's giving "retired but still serving" 😭

On the original BSD implementation, and before glibc 2.2.2, the return type of this function is void. The POSIX version returns int, and this is also the prototype used since glibc 2.2.2.

Only the EINVAL error return is documented by SUSv2 and POSIX.1-2001.

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💜 CAVEATS 💜

okay this is the part where we slow down 👀

The interaction of this function with the SIGALRM signal, and with other timer functions such as alarm(2), sleep(3), nanosleep(2), setitimer(2), timer_create(2), timer_delete(2), timer_getoverrun(2), timer_gettime(2), timer_settime(2), ualarm(3) is unspecified.

unspecified means nobody promised you anything, fr fr. keep your timers apart, bestie 🙏

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🌈 SEE ALSO 🌈

alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2), sleep(3), ualarm(3), useconds_t(3type), time(7)

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and that's the whole page, mwah 💋 this one came straight outta Linux man-pages 6.20, dated 2026-02-08, and it's the usleep(3) girlies' official lore. go take a nap (for at least usec microseconds) 🌙💖